In Abandoned Earth, players control a robot who, having been switched on after a spaceship emergency, finds that everything has gone terribly wrong. There's no trace of human life and the rest of the electronic equipment is not working. Luckily, your character is armed with a service weapon.
It's essentially a first person shooting game inspired by (according to the programmers themselves) Bioshock, Half-Life, and Halo. The gameplay is similar to many other classic wave mode games, which include many popular shooting games. That's to say, players will face off against waves of enemies that get harder and harder to defeat while improving their abilities and picking up new weapons.
Abandoned Earth is a good free FPS that offers very addicting gameplay and spectacular graphics. You'll need a good computer in order to take advantage of them. If your computer is older, you'll have to work with graphics at a lower setting.